THE RELEASE OF H³-NOREPINEPHRINE IN ARTERIAL STRIPS STUDIED BY THE TECHNIQUE OF SUPERFUSION AND TRANSMURAL STIMULATION

¹ Department of Pharmacology, UCLA School of Medicine, Los Angeles, California

The release of tritiated norepinephrine (H³-NE) was studied in relation to muscle contraction in the isolated rabbit main pulmonary artery. This artery was cut spirally into a strip, labeled with dl-H³-NE and superfused with Krebs-bicarbonate solution. Excitation of the nervous elements by electrical transmural stimulation caused contraction and a sharp rise in the overflow of H³-NE. Both these responses were blocked by tetrodotoxin and bretylium. Of the total tnitium activity in the superfusate, during rest approximately 30% and during stimulation 50% was accounted for by H³-NE. The remainder was attributable to metabolic products of which the non-catechols predominated over the deaminated catechols. In the presence of phenoxybenzamine, the transmural stimulation-induced tritium overflow and the proportion of intact H³-NE were greatly elevated. The overflow declined rapidly upon continued stimulation. The combination of superfusion and transmural stimulation may be of value for concurrent measurement of the neurotransmitter release and effector cell response in a number of tissues.

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